Process of making spheroidal gel particles



y 1949- J. A. ANDERSON ETAL 2,468,357

PROCESS OF MAKING SPHEROIDAL GEL PARTICLES Filed Nov. 29, 1945 n a y w ,r e w .m giwumq mw m V v r 4 m 8 n i 1 m Q Q w a w 7 E30 h isawaog 9803a Ebho B mi PateritedMaySJMQ PROCESS OF MAKING SPHEROIDAL GEL PARTICLES John A. Anderson, Chicago, and Vanderveer Voorhees, Homewood, Ill., assignorsto Standard Oil Company, Chicago, 111., a corporation of In- Application November 29, 1945, Serial N... 631,769

Claims. (Cl. 252-448) .This invention relates to the manufacture of solids in the form of mlcrospherical particles and it relates particularly to the manufacture of microspheroidal gelv particles useful as catalysts and adsorptive agents. It has heretofore been of the equipment by abrasion is greatly reduced by the use of said solids in the form of smooth rounded particles which may be spheres or spheroids. The problem occurs particularly in the decolorizing of oils, cracking of petroleum, hydroforming of naphtha, polymerization of gases and in hydrocarbon conversion processes generally. The movement of solids in these systems may be in a mass or moving bed or in dense or dilute phase suspension.

Various methods have been proposed and employed heretofore for the manufacture of spheroidal particles and it has been found that the metal oxide gels such as silica gel, alumina gel, magnesia-silica gel, chromium oxide gel, and various combinations of metal oxides in the form of their gels can be prepared in unusually strong particles by coagulating droplets of the respective sols or other solutions and thereafter drying and igniting, sometimes employing a washing step to remove undesirable water-soluble salts. In the preparation of the droplets of sol for making spheroidal gel particles, several methods have been devised including injecting droplets of the spherical particles rather than larger gel parti-' cles. The microspherical particles referred to herein are particles having a diameter in the range of about 20 to 300 microns when gelled and dried, although considerably smaller parti-' cles can be prepared by this method whendesired, i. e. particles having diameters of the order of two to ten microns. For most purposes, particularly for the conversion of hydrocarbons by contacting fluidized masses'of catalyst particles, it

is preferred to employ particles having diameters above 20 microns, preferably above 40 to 50 microns, in order to facilitate the recovery of the catalyst from suspension in the vapors and gases by reason ofthe increased settling rate of the larger particles. For example in catalytic cracking with fluidized solids it is necessary to remove carbonaceous deposits from the catalyst at frequent intervals which can be done by transferring it to a regenerating zone where it is contacted with air, for example at 1000 to 1200 F., requiring the catalyst to be recovered from the spent regeneration gas before discarding it to the flue. Where catalyst particles of more than 20 microns diameter are employed, the catalyst can be recovered from the flue gas by the simple use per cubic foot. The transfer of catalyst in highvelocity streams from one part of the apparatus to another also serves to break down the catalyst particles and reduce them to a point where it is diflicult to longer recover the particles and they are quickly lost from the system. The lossof catalyst from the hydrocarbon conversion system which normally recycles 2 to 5tonsof catalyst per ton of oil treated and may recycle as much as 20 or 25 tons of catalyst per ton of oil treated, forms a major part of the cost of operating such processes and may be as much as 1 to 5 pounds per barrel of oil treated. It is therefore very important to employ catalyst in the form of particles having high physical strength and resistance to abrasion and crushing. The use of catalyst in the form of spheroidal 'gel particles has proved very advantageous for this reason.

In the preparation of microspheroidal gels by the spray technique, in which a solution is dispersed in a gaseous medium, we have discovered that a large portion of the particles are imperfect in that they contain bubbles of gas which greatly weaken the particles, reducing their average density and rendering them subject to easy fracture by crushing. The gas bubbles in the microspherical particles are not readily observed by the naked eye but can be detected easily by microscopic examination. The object of our invention is to preparemicrospheroidal particles of gel which are solid throughout by employing a modification of the spray technique wherein a gel-producing solution of sol is sprayed into an atmosphere of vapor or gas. According to our invention, we surround the spray at the point of particle formation with a condensable vapor, that is. we substantially exclude noncondensable gases from the region where the sol particles are produced.

Our invention is illustrated by a drawing in which Figure 1 shows diagrammatically one form ef'apparatus for producing solid gel particles by spraying a solution into a chamber substantially free from noncondensable gases. Figure 2 shows another form'of apparatus in which only the atmosphere immediately adjacent the spray nozzle is maintained free from noncondensable gases. Figure 3 is a modified form of the apparatus shown in Figure 2.

Referring to Figure 1, a suitable solution for the preparation of gels is introduced by line ID to spray nozzle II. This nozzle may be of the mixing type similar to that shown in U. S. patent of Marisic, 2,384,946, or if the solution used be a sol ready to gel without further mixing, the nozzle may be of the liquid ejector type in which a line stream is ejected at high velocity from a vortex. We may employ a fast rotating disk onto which the sol is allowed to flow in a stream and thrown oif the periphery at high velocity. If an aspirator type spray is used, it is necessary to employ a condensabl vapor as the aspirating fluid therein.

The solution supplied by line I may be any suitable gel such as silicic acid sol, alumina sol, etc., or two solutions may be supplied to the mixer spray head I I wherein the solutions are mixed and ejected in the form of a sol which quickly sets to a gel. Thus, a solution of sodium silicate and acid or sodium silicate and aluminum sulfate may be mixed for this purpose. The sol or other mixture of solutions is referred to herein as a gelable solution, i. e. one which will gel of itself.

The spray nozzle II is located within chamber I2 which is of suificient diameter to prevent the impingement of sprayed particles on the walls and of suflicient height to allow the particles of sol or other solution to become solidified before striking the bottom. It is preferred that chamber I2 be a tower of sufficient height to keep the particles in suspension until they have largely dried and become free flowing so that they can be easily removed at outlet I3 through valve I4 leading into vestibule I5 communicating with outlet valve I6 in order that the particles may be withdrawn without permitting access of the external atmosphere to the interior of chamber I2. Heat for drying the particles can be supplied by a heating jacket I! surrounding chamber I2 and supplied by steam through line I8. Line I9 is a vent to the steam jacket and line 20 is a condensate discharge. When drying the gel within the tower it is preferred to supply heat at a lower section, allowing suflicient space above the heated section for the particles of gel to form from the solution injected at the top. Instead of drying the gel particles to a free-flowing mass, they may be partly dried and collected in an oil bath at the bottom of tower I2, the resulting slurry being removed from time to time or continuously through a suitable valve arrangement.

The atmosphere within chamber I2 is maintained substantially free from uncondensable gases by exhausting through line 2| to vacuum pump 22. The reduced pressure in chamber I2 may be maintained as low as 50 to 100 mm. mercury absolute when operating at normal temperatures but by operating at somewhat elevated temperatures the degree of vacuum need not be very high. Thus, when operating at a temperature of about 150 F. the absolute pressure may be of the order of 3.5 p. s. i. within chamber I2 and when operating at about 175 F. the pressure within chamber I2 may be about 7 pounds per square inch absolute, that is, about one-half atmosphere. The pressure employed will generally be somewhat below that which corresponds to the vapor pressure of water at the temperature of the tower.

When discharging the catalyst from chamber l2 through vestibule I5, valve I4 may be opened to admit into vestibule I5 a quantity of catalyst which will ordinarily be freeflowing, somewhat like sea sand in its general appearance. Valve I4 is then closed and valve I6 opened to discharge the catalyst from the apparatus. Vacuum pump 23 is employed to exhaust vestibule I5 and it is usually desirable to maintain the pressure in I5 below that of chamber I2 at the time the solids are being transferred from chamber I2, in order to avoid any possibility of noncondensable gas gaining access to chamber I2 where it will interfere with the formation of the uniformly solid particles of gel. Manometers 24 and 25 serve to indicate the pressures existing in chambers I2 and I5 respectively.

It is ordinarily not serious if the particles contain small enclosures of uncondensable gas, which will result if the composition of the atmosphere within chamber I2 includes some uncondensable gas. Thus, a very small enclosure of fixed gas within the catalyst gel particles may result by operating with an atmosphere consistin of about 5 to 10 per cent air and per cent water vapor by volume.

Although operation with the apparatus shown in Figure 1 is preferably conducted at pressures below atmospheric; this is not essential and we may operate at higher pressures, e. g. 10-100 p. s. i. with good results. ticles produced are usually in the hydrogel form. No vacuum pump is needed when using pressure above atmospheric but instead a supply of steam or other condensable vapor is required to fill the gelling chamber.

In order to avoid admission of uncondensable gases in solution in the sol or other solution supplied through line I0, we may previously exhaust this solution by boiling or by subjecting it to a vacuum suificient to pull off dissolved gases.

In the apparatus shown in Figure 2, a closed system is not required but the spray tower 30 is open to the atmosphere at the bottom and may be connected by line 3| to a suitable exhaust means, for example to a flue. Atmospheric pressure is employed. As in the case of chamber I2, tower 30 is of suflicient diameter to avoid impingement of spray on the walls thereof. In the drawing it is indicated as of cylindrical form but it may also be of any other suitable shape; for example it may be a large rectangular room or chamber, preferably of sufficient height to permit drying the particles of gel before reaching the bottom. Tower 30 may also be heated by various means such as a heating jacket if desired.

The sol or solution is supplied by line 32 leading to nozzle 33 where the solution is dispersed in the upper part of the tower. Surrounding the nozzle we may employ a baflie or collar 34 into In this case, the parwhich a currentof steam or other condensable vapor is led by line 35. In place of. steam we may use alcohol vapor, methanol vapor, naphtha vapor, ethyl ether vapor, or thevapor of. any suitable low boiling solvent which will condense under the conditions existing in a spray tower before the droplets of sol or other solution become solidifled to a gel. The collar 34 is for the purpose of retaining the vapor around the nozzle and thus preventing contamination of the dispersed particles of solution by contact with fixed gases, for example air.

Drying of the sprayed particles is effected by contact with air or other drying gas which is introduced by line 36. Where the drying agent is air it is only necessary to allow free access of air, for example warmed air, to the base of tower 30 which may be open to the atmosphere. The solidified and preferably dried gel particles fall through the tower and alight on the upper surface of belt conveyor 31 which is travelling upwardly in the direction of the arrow. Perfect or nearly perfect spherical particles roll freely downward against the motion of the conveyor and are caught in receiver 38, while irregular particles and particles which are improperly dried and which adhere to the conveyor are removed by scraper 39 and fall into receiver 40. By proper adjustment of the conditions and the spray, the formation of imperfect particles is largely avoided.

Figure 3 illustrates an alternative arrangement of the upper part of tower 30. In this modification, hood or collar 34 is dispensed with and steam is supplied directly by line 4| to the top of tower 42 which is preferably insulated by lagging 43.- A suitable solution of sol is injected by line 44 to nozzle 45 and the spray is formed in an atmosphere consisting substantially entirely of steam or other condensable vapor. The steam escapes from the tower by line 46 which may lead to an exhaust vent or flue. Air or other drying gas sup plied to the tower is discharged therefrom along with the excess steam used to blanket the top of a the tower. It is desirable that the specific gravity of the steam or other vapor in the top of the tower be less than that of the drying gas in the lower part of the tower in order to avoid undesirable mixing orv inversion of the vapors and gases.

In the apparatus described in Figures 2.and 3, a drying gas flowing upwardly through towers 30 amass? of fixed gases within-the particles but also provides a means for controlling the rate of drying during the gelling of the particles. 1

When employing silica sol free of'alkali' metal.

. ready for use in hydrocarbon conversion without or42 which may be previously freed of moisture in order to accelerate its drying effect, may also or alternatively be heated to a somewhat elevated temperature, e. g. 150 to 250 F..or higher, care being taken to avoid heating the gel particles to a temperature atwhich they are damaged by excessive rate of evaporation of moisture therefrom. Since the particles prepared by our process are solid throughout, they can be subjected to more rapid heating without rupture than is the case with solids containing trapped uncondensable gases which expand and rupture the particles on heating or which act as nuclei for the liberation of steam.

The heated vapors supplied by lines 35 and 4| have the effect of hastening the gelling of the. sprayed particles of solution or sol. Where steamv is employed it serves to prevent drying' of the particles of sol before gelation has occurred, thus avoiding the formation of a skin or envelope of gel around each particle which is later subject to wrinkling and distortiomby irregular shrinking condensable vapor occluded withinsaid droplets of the gel on drying. The use of an atmosphere washing. The dried gel from the gelling chamber passes directly to an ignition step where 'it'is heated to about 10001200 F. for several hours, then cooled and charged to the conversion process. The term condensable vapors used in this application includes vapors having boiling points above the temperature under consideration and also water-soluble gas which dissolves in the hydrogel at the conditions of gelling. The term includes any vapor or gas which reverts to the liquid phase at the gelling conditions.

Having thus described our invention what we claim is: I

1. The process of making solid spheroidal par ticles of an inorganic oxide gel whichcomprises sprayingan inorganic oxidesol, capable of gelling,

into an atmosphere of condensable vapor sub stantially free of noncondensable gases, forming said 501 into spheroidal droplets within said atmosphere and, while said droplets are still liquid, condensing vapors included therewithin, maintaining said droplets in suspension for a period of time sufficient to permit gelling and thereafter drying the resulting gel particles.

2. The process of claim 1 wherein said atmosphere consists substantially entirely of steam.

3. In the process of preparing microspheroidal particles of an inorganic oxide gel substantially free from gas inclusions normally obtained when agelable inorganic oxide sol is sprayed into an atmosphere of gas and allowed to gel therein, the

improvement comprising spraying said gelable aqueous solutionzin the form'ofspheroidal droplets into an evacuated zone from whichair and said droplets followed by complete gelation and solidification thereof and thereafter drying the gel particles; I I

4. The process of claim 3 wherein said gelable solution is a silicic acid sol.

' 5. The process of preparing an inorganic oxide gelin the form of small solid spheroidal particles. substantially free from-.gas'incluslons which com- I prises dispersing a gelable inorganic'oxide So] in' the form of small spheroidal droplets in the upper part of a gelling zone, maintaining in the top of v said gelling zone a vaporsusbtantially entirely condensable at the conditions of temperatures and pressure existing within said droplets at the time of gelling, maintaining in the lower part of said gellin zone an atmosphere of a drying gas" for removing water from descending gel particles, said drying gas being prevented by said vapor from contacting said droplets of solution during their formation, and effecting condensation of before solidification, and removal of water therefrom.

caused to flow downwardly from the topof said gelling zone concurrently with said particles and said drying gas is caused to flow upwardly from the bottom of said gelling zone countercurrently', to said particles, sald'vapor and said gas'bei'ng 6. The process of claim 5 wherein said vapor is 7 withdrawn from said zone at an intermediate Number point between top and bottom thereof. 1,755,496 JOHN A. ANDERSON. 1,843,576 VANDERVEER VOORHEES. 2,137,213 5 2,295,595 REFERENCES CITED 2 316 70 The following references are of record in the 21384946 me of this patent: gig-gig UNITED STATES PATENTS m Number Name A Date 1,501,376 Wreesman July 15, 1924 1,506,118 Govers Aug. 26, 1924 a Name I Date Behrman Apr. 22, 1930 McClure Feb. 2, 1932 Clayton et a1. Nov. 15, 1938 Mills Sept. 15, 1942 Colgate et a1. Apr. 13, 1943 Marlsic Sept. 18, 1945 Stephanott Dec. 31, 1946 Archibald Feb. 3, 1948 Certificate of Correction Patent No. 2,468,857. May 3, 1949.

JOHN A. ANDERSON ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 3, line 27, after the word may insert also; line 34, for gel read sol; column 6, line 48, claim 3, after the insert resulting;

and that the said Letters Patent should be read with these corrections therein that the same mayconform to the record of the case in the Patent Ofiice.

Signed and sealed this 11th day of October, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

